Possible workaround for shadow catcher EIS problem

[1funk]

There was a discussion on the skype channel about shadow catcher not working correctly with EIS (it has been mentioned in a few threads)

Vladimir Nedev posted a link to a max setup which gave me some clues on how to do this in modo.

UPDATE: I found a problem with this method and created an updated scene in the post below
http://forums.chaosgroup.com/showthr...045#post722045



In modo you need:
1. An invisible (spherical) dome light for the diffuse lighting, which affects everything
2. Another invisible (spherical) dome light for reflections only. You use light linking to exclude the shadow catcher (which you put in a group)
3. An environment, set to visible to camera only
4. The shadow catcher needs V-Ray object properties with matte surface enabled and alpha contribution = -1

It "should" work with only 2 dome lights, but for some reason, this doesn't work in modo and needs the environment too. The trick was to make sure the dome light radiance matched the environment image. I did this by eye (toggling the dome visibility on and comparing to the environment) and found dome radiance of 6.5W was roughly equal to environment intensity of 1.0W

I'm not completely sure this setup is correct, but I thought it was worth posting a sample scene here.

[boyan]

There was a discussion on the skype channel about shadow catcher not working correctly with EIS (it has been mentioned in a few threads)

Vladimir Nedev posted a link to a max setup which gave me some clues on how to do this in modo.

In modo you need:
1. An invisible (spherical) dome light for the diffuse lighting, which affects everything
2. Another invisible (spherical) dome light for reflections only. You use light linking to exclude the shadow catcher (which you put in a group)
3. An environment, set to visible to camera only
4. The shadow catcher needs V-Ray object properties with matte surface enabled and alpha contribution = -1

It "should" work with only 2 dome lights, but for some reason, this doesn't work in modo and needs the environment too. The trick was to make sure the dome light radiance matched the environment image. I did this by eye (toggling the dome visibility on and comparing to the environment) and found dome radiance of 6.5W was roughly equal to environment intensity of 1.0W
I'm not completely sure this setup is correct, but I thought it was worth posting a sample scene here.

Aloha Funky,
Thank you for the feedback. About the shadow catcher I highly recommend to you use V-Ray Object Properties for more control. My workflow is here: http://community.thefoundry.co.uk/di...?id=58287&t=20. Hope is workable for you, also.

BR Boyan

[1funk]

Hi Boyan,

I just tested your method with the scene I posted. It works OK, but there are a couple of problems.

1. It removes the teapot reflection in the ground. Not everyone needs the reflection though.
2. The alpha channel is incorrect (which can be fixed by setting alpha contribution to -1, which Im doing in the sample scene)

Thanks for the video

[1funk]

I have also found a problem with my method, which I didnt notice with the HDRI I'm using.

If you make the teapot very reflective, you can see a dark black line along the horizon in the reflection.

So I guess we will have to wait for the changes in 3.5 to really have this working correctly.

[1funk]

I'm trying a different method which seems to fix the reflection/black horizon problem

Im only using 1 dome light now for diffuse lighting, and all the rest camera/reflection/refraction is done by the environment

In short:
- Turn V-Ray EIS OFF.
- Add a dome light with your HDR for diffuse lighting only (using the same 6.5W radiance as before to match 1.0W intensity of the environment).
- The environment HDR is set to camera/reflection/refraction rays only.
- The shadow catcher has matte surface enabled, and alpha contribution to -1

[boyan]

Well done Funk. You have to post into MODO forum also .

BR.Boyan

[1funk]

Well I'm not completely sure if this is "correct" either. I'm still too new to V-Ray.

With this method, we are basically using importance sampling for the diffuse lighting only. I don't know what is happening internally with the environment camera/reflection/refraction rays.

In MODO, EIS/MIS also has an affect on reflections. There is a channel (hidden from the UI) on the render item called "Environment MIS" which defaults to both "indirect diffuse" and "blurry reflections".

I'm not sure if V-Ray has any kind of MIS support for blurry reflections.

[vladimir.nedev]

Yes, we have, you will get more noise from blurry environment reflections, if they are not sampled using a Dome light.

Greetings,
Vladimir Nedev

[1funk]

OK thanks for letting me know Vladimir.

So I guess we really need to wait for 3.5 to get this working correctly

[1funk]

I'm curious if this issue was ever fixed in Next? Do shadow catcher and EIS work correctly now?